Field of the Invention
The invention relates generally to fracturing fluids that contain a flowback aid, and methods of fracturing a subterranean formation using fracturing fluids that contain a flowback aid.
Background of the Related Art
Hydraulic fracturing is a process that forms fractures in a subterranean formation using a pressurized fluid. The fracturing fluid is introduced into the subterranean formation through a wellbore that has been drilled into the formation, and then pressurized to fracture the formation. Among other components, the fracturing fluid will typically contain a proppant material that enters into the newly formed fractures and prevents those fractures from closing up.
At the end of a hydraulic fracturing job, a large surface-area fracture will have been created and propped permanently open by the application of a proppant-laden, pressurized, often aqueous, hydraulic fluid. The next step in the hydraulic fracturing job is to decrease the pressure applied to the aqueous hydraulic fluid to allow the fluid sitting in the near well-bore region of the target formation between the targeted hydrocarbons and the wellbore to flow back into the well and up to the surface for treatment and disposal or re-use later.
The amount of fracturing fluid left behind in the formation will diminish to an irreducible fraction and then stop flowing back. This irreducible fraction of fracturing fluid left behind in the formation will subsequently impede the flow of hydrocarbon from the petroliferous formation into the very high permeability proppant pack.
A flowback aid may be included in the fracturing fluid to reduce capillary pressure and water blocks, thereby improving the kinetics of the flowback and preventing or minimizing the leaving-behind of any substantial amount of the fracturing fluid. Flowback aids, such as surfactants, have also been shown to aid in the “clean-up” of the proppant pack, thereby accelerating the flow of hydrocarbons through the high permeability proppant pack, as well. Known flowback aids each have their own set of properties and may present a tradeoff of one beneficial property for another undesirable property. Determining the best flowback aid for a specific reservoir may involve multiple considerations.
Experience has demonstrated that a scientific measure of the ability of a flowback aid to change the wettability of the near wellbore formation or to reduce the water saturation in the pores of the targeted subterranean petroliferous formation can be obtained by accurately measuring the contact angle formed by the flowback aid within a capillary tube. In flowback tests on cores simulating the performance of an element of the reservoir under simulated in-situ conditions, experience has shown that capillary contact angles greater than 80° are correlated with the more efficient flowback of aqueous fluids (simulating those used in formation fracturing). Reducing the water saturation in the pores of the targeted subterranean petroliferous formation is desirable for increased production of oil or gas because the volume of the flow channel for oil or gas through the pores in the rock will be occupied, in part, by the immiscible water phase; and reducing the fraction of this volume that is occupied by water will necessarily increase the fraction of this volume that is available for flow by oil or gas.